Both CAT troff and ditroff need to know the width of each character
that you use. The widths of each character (along with some additional
characteristics) are arranged in a file for each font. There are
basically five different width table formats:
1) CAT troff: uses a binary table of 224 unsigned chars.
2) MIPS (and RISC/Ultrix) CAT troff uses an ASCII dump of (1)
3) DWB 2.x and several of the commercial variants use an ASCII
format that is compiled into a binary form by a special program
called "makedev".
4) DWB 3.x uses the ASCII format mentioned in (3) - doesn't need
to be compiled.
5) Groff uses the ASCII format mentioned in (4) with minor variations.
If the width tables are wrong, character spacing will look funny - up
to and including overlapping characters, and broken right justification.

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